In recent years in response to increasing demand for high frequency microwave oscillators, semiconductor elements, such as Gunn diodes or Impatt diodes, have been effectively utilized to develop the oscillators. While semiconductor microwave oscillators represent significant progress in the state of the art, in terms of size, simplicity, reliability, long life, etc., they have also presented certain shortcomings and problems of their own. For example, numerous applications require higher Q and better frequency stability. Significant progress has been made to overcome these shortcomings by numerous improved negative resistance microwave oscillators. Such an improved microwave oscillator is disclosed in the U.S. Pat. No. 3,913,035 issued on Oct. 14, 1975. As described therein the improved oscillator includes a semiconductor diode such as a Gunn or an Impatt diode located within a low Q resonance cavity for generating a carrier frequency, and a second resonance cavity tuned to the same frequency and having a very high Q relative to the first cavity and electromagnetically coupled to the low Q cavity. The microwave energy generated in the low Q cavity is coupled to the high Q cavity which reflects energy at the operating frequency back to the low Q cavity to maintain oscillations at this frequency, thereby enhancing the oscillator frequency stability. The microwave energy so developed is supplied to the load by a microwave passage that is coupled to the low Q cavity. An internal microwave load is employed to dissipate undesired frequencies thereby restricting these frequencies from being generated within the low Q cavity, thereby eliminating "moding."
While the aforementioned negative resistance high Q microwave oscillator of the aforementioned type provides stable frequency output, and advantages, it does not work with LSA devices. Avalanche breakdown occurs and prevents high Q oscillations from taking place. Therefore, there is still a need for higher Q semiconductor microwave oscillators that can utilize LSA devices, especially since higher pulsed peak power outputs can be obtained from LSA devices than from any other comparable type of negative resistace semiconductor device.